Legionella bacteria in cooling towers

Researchers from the Centers for Disease Control and Prevention (CDC) in the United States recently analysed water from 196 cooling towers, representing eight of nine continental US climate regions, for Legionella DNA.

They found 84% of the cooling towers from every region of the country had Legionella bacteria present or evidence it had been there at some point, with live Legionella bacteria found in 79 of the cooling towers.

Screening for Legionella DNA was done using multiplex real-time polymerase chain reaction and samples positive for Legionella were cultured. Resulting Legionella isolate species and serogroup were characterised using PCR, antibody testing and gene sequencing.

Between 2000 and 2014, the rate of reported cases of Legionnaires’ disease increased 286% in the US and cooling towers are known to be a major source of outbreaks. The CDC study is however, the first to show how widespread Legionella may be in these towers across the US.

The study was presented in April 2016 at a CDC conference in Atlanta by Dr. Anna Llewellyn and will be published in a peer-reviewed journal soon.

Anna told the Wall Street Journal, in a story published May 3, that just because a cooling tower has Legionella doesn’t necessarily mean it’s spreading disease. The researchers are hoping to conduct another study to determine what factors contribute to a cooling tower’s risk of becoming a source of an outbreak.